614 THE BLOOD-VASCULAR SYSTEM. 



venous plexus which covers the entire surface of the cord, being situated between 

 the pia mater and arachnoid. These vessels emerge chiefly from the median 

 furrows, and are largest in the lumbar region. Near the base of the skull they 

 unite and form two or three small trunks, which communicate with the vertebral 

 veins, and then terminate in the inferior cerebellar veins or in the inferior petro- 

 sal sinuses. Each of the spinal nerves is accompanied by a branch as far as the 

 intervertebral foramina, where it joins the other veins from the spinal canal. 

 There are no valves in the spinal veins. 



VEINS OF THE LOWER EXTREMITY, ABDOMEN, AND PELVIS. 



The Veins of the Lower Extremity are subdivided, like those of the upper, 

 into two sets, superficial and deep, the superficial veins being placed beneath the 

 integument, between the two layers of superficial fascia, the deep veins accom- 

 panying the arteries and forming the vense comites of those vessels. Both sets 

 of veins are provided with valves, which are more numerous in the deep than in 

 the superficial set. These valves are also more numerous in the lower than in 

 the upper limb. 



The Superficial Veins of the Lower Extremity are the internal or long saphen- 

 ous and the external or short saphenous. 



On the dorsum of the foot is a venous arch situated in the superficial struc- 

 tures over the anterior extremities of the metatarsal bones. It has its convexity 

 directed forward, and receives digital tributaries from the upper surface of the 

 toes ; at its concavity it is joined by numerous small veins which form a plexus 

 on the dorsum of the foot. The arch terminates internally in the long saphenous, 

 externally in a short saphenous vein. 



The internal or long saphenous vein (Fig. 334) commences at the inner side of 

 the arch on the dorsum of the foot ; it ascends in front of the inner malleolus 

 and along the inner side of the leg, behind the inner margin of the tibia, accom- 

 panied by the internal saphenous nerve. At the knee it passes backward behind 

 the inner condyle of the femur, ascends along the inside of the thigh, and, pass- 

 ing through the saphenous opening in the fascia lata, terminates in the femoral 

 vein about an inch and a half below Poupart's ligament. This vein receives in 

 its course cutaneous tributaries from the leg and thigh, and at the saphenous 

 opening the superficial epigastric, superficial circumflex iliac, and external pudic 

 veins. The veins from the inner and back part of the thigh frequently unite to 

 form a large vessel, which enters the main trunk near the saphenous opening ; 

 and sometimes those on the outer side of the thigh join to form another large 

 vessel ; so that occasionally three large veins are seen converging from different 

 parts of the thigh toward the saphenous opening. The internal saphenous vein 

 communicates in the foot with the internal plantar vein ; in the leg, with the 

 posterior tibial veins by branches which perforate the tibial origin of the Soleus 

 muscle, and also with the anterior tibial veins ; at the knee, with the articular 

 veins ; in the thigh, with the femoral vein by one or more branches. The valves 

 in this vein vary from two to six in number ; they are more numerous in the 

 thigh than in the leg. 



The external or short saphenous vein (Fig. 335) commences at the outer side 

 of the arch on the dorsum of the foot ; it ascends behind the outer malleolus, 

 and along the outer border of the tendo Achillis, across which it passes at an 

 acute angle to reach the middle line of the posterior aspect of the leg. Passing 

 directly upward, it perforates the deep fascia in the lower part of the popliteal 

 space, and terminates in the popliteal vein, between the heads of the Gastro- 

 cnemius muscle. 1 It receives numerous large tributaries from the back part of 



1 Mr. Gay calls attention to the fact that the external saphenous vein often (he says invariably) 

 penetrates the fascia at or about the point where the tendon of the Gastrocnemius commences, and runs 

 below the fascia in the rest of its course, or sometimes among the muscular fibres, to join the popliteal 

 vein. (See Gay on Varicose Disease of the Lower Extremities, p. 24, where there is also a careful and 

 elaborate description of the branches of the saphena veins.) 



